Air brick: Could the hole be made bigger than 225mm?

[Ambergreen45]

I want to fit an air brick 225 x 140mm. I took one brick out of one of the walls on the inside of the property, but now I want the hole to be slightly on the left. I want to take 3/4 of the brick next to the one I have just taken out which would make the horizontal hole at about 394mm in lenght. Is it safe to do that? If I have to put part of the brick back on before proceeding, how long will I have to wait before the mortar is fully dry?

Other info: the upstairs is a suspended concrete floor and it looks like the beams seem to rest on the wall next to it; cavity wall; the brick I took out is from the fourth row starting from the ceiling.

Many thanks!

 

[^woody^]

How are you going to deal with the liner?

Mortar dries in a day

 

[Ambergreen45]

The wall is brick, cavity with no insulation, and then brick. The hole is on one side of the internal wall forming part of the length of the room. I've taken a small part of plaster on the ceiling that joins the adjoining wall (forming part of the width of the room) and saw the concrete beams rest on the internal brickwork.

Maybe the safest bet is to put 3/4 of a brick back with mortar (I will have a little gap the size of 1/4 of a brick), let it dry for a day and then correct it by taking 3/4 off the next brick on the left to finally make the length of the hole 225mm?

That will then be in line with the external bricks before making a hole on the outside wall to be able to insert the liner. I suppose I should have started on the outside...

Thank you.